Patent Document 1, Japanese Examined Patent Publication (kokoku) 3-20451 discloses aluminum-based bearing alloy based on the Al—Sn—Si fundamental components. This aluminum-based bearing alloy contains from 3 to 20% of Sn, from 0.1 to 1% of Zr, from 1.5 to 8% of Si, from 0.2 to 2% of one or more of Cu and Mg, and from more than 0.1 to 1% of at least one of V, Nb, Mo and Co plus Zr in total. The bearing alloy is in sliding contact with a hardened steel shaft of a cast-iron shaft. That is, no solid-lubricant coating is applied on the bearing alloy.
Aluminum-based bearing alloy, which is subjected to heavy load, is provided with an overlay, which is based on soft metal, such Sn, Pb and the like, in order to ensure compatibility. Patent Document 2, Japanese Unexamined Patent Publication (kokai) No 4-83914 proposes a solid-lubricant coating, which can substitute for the soft-metal based overlay. Subsequent improvements of this solid-lubricant based overlay have been published in Tribology Association of Japan under the title of “Aluminum Bearing Fitted With Solid-Lubricant Overlay” (1st through 4th series). This solid-lubricant layer of the bearing consists of from 90 to 55% by mass of the solid lubricant, such as MoS2, BN, WS2, graphite and the like, and from 10 to 45% by mass of the polyimide based binder. The solid lubricant may be replaced with from 1 to 20% by mass of the friction controlling agent, such as CrO2. The aluminum-based bearing alloy with the solid-lubricant overlay and the same alloy with the lead-alloy based overlay are tested to evaluate the fatigue resistance, the wear resistance and the seizure resistance. The experimental data of fatigue resistance and wear resistance of the former alloy is equivalent to those of the latter alloy. The seizure resistance of the former alloy is exceedingly superior to that of the latter alloy. The solid-lubricant layer of the aluminum-based bearing layer is prepared by spraying the solid lubricant, diluting agent and the polyimide-based binder, drying and baking. The solid-lubricant layer is bonded on the underlying aluminum alloy.
Patent Document 3, Japanese Patent No. 3,733,539 proposes an aluminum bearing with the solid lubricant overlay. The aluminum-based bearing alloy has from 1.0 μm to 4.3 μm of the surface roughness Rz. On this surface is applied a 3 to 8 μm thick solid-lubricant layer, which has 5 μm or less of surface roughness Rz and which consists of from 98 to 55% by mass of solid lubricant and from 2 to 45% by mass of the thermosetting resin. In the manufacturing method of the aluminum bearing with the solid lubricant overlay, the surface of the aluminum-based alloy bearing is cleaned, by for example, alkaline degreasing, water-rinsing, and hot-water rinsing. The surface roughness of the aluminum-based alloy is also adjusted. The spraying described in Patent Document 2 is carried out to form a coating layer subsequent to the surface cleaning and the adjusting of the surface roughness. Patent Document 3 describes the sliding properties of the aluminum bearing with the solid-lubricant overlay as follows. (a) The compatibility is better with the increase in the amount of solid lubricant in the solid-lubricant layer. (b) The seizure resistance is impaired when the thickness of a coating exceeds 10 μm. (c) The sliding properties of a thin coating layer are influenced by the surface roughness of the underlying aluminum alloy, when the coating layer becomes thin. Therefore, the seizure resistance is impaired.
Patent Document 4, Japanese Patent No. 3,133,209 proposes a solid-lubricant overlay, which consists of from 70 to 97% by mass of the solid lubricant selected from MoS2, WS2, BN, graphite and carbon fiber, and from 3 to 30% by mass of binder. This composition for forming the lubricant film contains a large proportion of the solid lubricant. The binder must hold a large proportion of the solid lubricant and therefore consists of polyimide based binder and compound having epoxy group. The composition for forming a lubricant film is applied on the surface of bearing alloy by spraying.
Patent Document 5, Japanese Unexamined Patent Publication (kokai) No.2002-53883 proposes a solid-lubricant overlay, which consists of polyamide-imide resin as well as solid lubricant and wear-resistant agent dispersed in the polyamide-imide resin. The polyamide-imide resin is characterized by having from 78.4 to 98 MPa of the tensile strength, from 1960 to 2940 MPa of the Young's modulus and from 10 to 20% of the elongation. This sliding member composition is suited for sliding member operated in lubricating oil, such as a piston skirt. The sliding member composition is sprayed to form a solid-lubricant overlay.
Patent Document 6, Japanese Unexamined Patent Publication (kokai) No. 2002-61652 proposes a solid-lubricant overlay consisting of from 70 to 30% by volume of thermo setting resin and from 30 to 70% by volume of solid lubricant (total of the thermosetting resin and the solid lubricant is 100% by volume). The thermosetting resin used in this overlay is soft and exhibits high elongation at high temperature. Specifically, the thermosetting resin exhibits from 70 to 110 MPa of tensile strength and from 7 to 20% of elongation at 25° C. and 15 MPa or more of tensile strength and 20% or more of elongation at 200° C. The solid-lubricant layer has Hv 20 or less of hardness. According to this proposal, soft thermosetting resin having high elongation at high temperature attains improved initial conformability at high speed. The solid-lubricant layer is prepared by the same method as in Patent Document 3. A method for forming the solid-lubricant overlay may be spraying and also roll transferring, tumbling, immersion, brush application, printing and the like.
The aluminum bearing with solid lubricant overlay proposed in Patent Document 7, Japanese Unexamined Patent Publication (kokai) No. 2004-263727 is the same as that proposed in Patent Document 6, except that the glass transition temperature of the resin is 150° C. or more.
The conventional copper-based sliding bearing alloys are mainly based on the Cu—Pb. Since Pb is environmental pollutant element, Cu—Bi based sliding bearing alloys, in which the Pb of the Cu—Pb alloy is replaced with Bi, have been proposed in for example, Patent Document 8, Japanese Unexamined Patent Publication (kokai) 56-142839, and Patent Document 9, Japanese Unexamined Patent Publication (kokai) No.11-29368, and Non-Patent Document 1, Tribologist (in Japanese) Vol. 51/No.6/2006, pages 456-462 “Current Conduction and Friction Characteristics of Copper-Based Sintered Alloy, in which Bi is Added”.    Patent Document 1: Japanese Examined Patent Publication (kokoku) Hei 3-20451    Patent Document 2: Japanese Unexamined Patent Publication (kokai) No. Hei 4-83914    Patent Document 3: Japanese Patent No. 3733539    Patent Document 4: Japanese Patent No. 3133209    Patent Document 5: Japanese Unexamined Patent Publication (kokai) No.2002-53883    Patent Document 6: Japanese Unexamined Patent Publication (kokai) No. 2002-61652    Patent Document 7: Japanese Unexamined Patent Publication (kokai) No. 2004-263727    Patent Document 8: Japanese Unexamined Patent Publication (kokai) No. 56-142839    Patent Document 9: Japanese Unexamined Patent Publication (kokai) No. 11-293368    Non-Patent Document 1: Tribologist, Vol. 51/No.6/2006, pages 452-462 “Current Conducting and Friction Properties of Copper-Based Sintered Alloy with Bi Addition”    Non-Patent Document 2: Tribologist Vol 50/No.9/2005, page 664 “Reviewing Fifty Years of Engine Bearings, Usually Referred to as Metal”